Focal amplifications involving chromosome 8p11-p12 occur in approximately 15% of human breast cancers. The fibroblast growth factor receptor 1 (FBFR1) gene has long been considered to be the best candidate oncogene at that locus. Three breast cancer cell lines developed in our lab; SUM-44, SUM-52 and SUM- 225, have overlapping amplicons centered around chromosome 8p11.2. FGFR1 is amplified in two of these cell lines, but is over expressed in only one of them. A second gene that maps to this region, transformation associated coiled-coiled protein 1 (TACC1), has recently been shown to be over expressed in some breast cancer cells and to have transforming activity in NIH3T3 cells. TACC1 is amplified and over expressed in all three of our cell lines. In addition to the FGFR1/TACC1 locus, SUM-52 and SUM-225 cells may each have distinct amplicons that center around 8p12 and 8q11.1 respectively. These regions contain several genes that are highly over expressed. Therefore, the broad aim of this proposal is to examine the prognostic and predictive significance of the 8p11-p12 amplicon in human breast cancer, and to identify genes therein that may be good targets for the development of novel therapeutics. The specific aims of this project are: 1) To complete the fine mapping of the 8p11-p12 amplicon in the SUM-44, SUM-52, and SUM-225 cell lines by Southern blotting using probes for genes known to map to the region of gene amplification in each line, 2) To examine the expression levels of the amplified genes in each cell line by northern blot and RT-PCR, 3) To determine the predictive and/or prognostic significance of amplification of distinct regions of the 8p12-8q11 amplicon, and of specific candidate breast cancer genes, in breast cancer specimens using tissue micro arrays, 4) To test the mechanistic significance of genes found to be amplified and over expressed in the three breast cancer cell lines by transduction of candidate genes into immortalized human mammary epithelial cells, and by antisense techniques to down-regulate over expressed genes in breast cancer cells. Thus, these studies are aimed at defining new and better prognostic and predictive markers for an important subset of breast cancer, and at identifying causally relevant genes the products of which could be good targets for novel therapeutics.